1. Field of the Invention
The present invention relates to a rocking piston type compressor in which a piston is rockably and slidably disposed within a cylinder.
2. Related Art
As a piston which is used in a compressor, there is known a rocking piston which is allowed to reciprocate within a cylinder while it is being rocked. In this type of rocking piston, a lip ring is provided on a leading end portion of a piston rod and the lip ring is used to seal up between the cylinder and the piston rod.
The seal performance of the lip ring becomes worse as it is used continuously. Specifically, the lip ring can be deformed due to an influence of a compression heat or a load applied thereto when it is pressed against a wall surface of the cylinder, or can be worn due to a continuous use thereof. Due to this, a seal performance of the lip ring is deteriorated and a compression efficiency is thereby deteriorated.
Even in the case that the seal performance of the lip ring is deteriorated, in a continuously working state of the lip ring, the lip ring is thermally expanded due to the compression heat, whereby the seal performance can be maintained. However, in an initial operation state of the lip ring, or in the case that the lip ring is used in a cold district where the lip ring is also cooled, the seal performance becomes worse until the lip ring is thermally expanded. Also, in the case that a motor of a small output is used, or in the case that the number of rotations of a motor is decreased for a purpose of quietness, a vertical movement of a piston becomes slower, whereby the lip ring is cooled due to an air leaking out from a clearance between the piston and lip ring and thus the seal performance thereof is hard to enhance.
In order to solve the above problems, according to the invention disclosed in Patent Reference 1, there is disclosed a structure in which a lip portion of a piston ring is energized toward a cylinder by an energizing member to thereby seal up between a piston main body and cylinder.
Patent Reference 1: JP-A-09-068279
Here, in the above-mentioned rocking piston, since the piston portion thereof rocks within the cylinder to thereby vary a space between the piston portion and cylinder, in most cases, there is used a flexible lip ring. Thus, in the case that such rocking piston is used in a compressor of a high pressure, the flexible lip ring cannot withstand a load of the high pressure and is thereby deformed, whereby the air leaks from a space between the lip ring and cylinder and thus the compression efficiency is thereby lowered. Therefore, in a conventional compressor, the rocking piston is used in a compressor of a low pressure. In the compressor of the high pressure, the rocking piston is not used.
On the other hand, since the rocking piston is simple in structure, it is hardly out of order and is inexpensive. Therefore, the conventional rocking piston has been required for improvement in order that it can be employed in a compressor of a high pressure. However, in attaining this object, it is necessary to use a lip ring having a large thickness.
However, according to the structure in Patent Reference 1, the piston ring for sealing up between the piston main body and cylinder is a ring having a circular flat plate-like shape in which its lip portion is bent and deformed upwardly in order to press a back-up ring (an energizing member) inwardly. Due to this structure, since the back-up ring (an energizing member) is caused to energize a vicinity of a bent portion of the piston ring. Thus, if that the piston ring is a flexible one, the back-up ring is able to energize the flexible piston ring. However, if the piston ring has a rather large thickness, the back-up ring is incapable of energizing the piston ring.